Telephone exchanges with speech store equipment are already known and are usually called voice mail equipment or devices in the technical language. Such devices are described in great detail in EP 0,087,849 and in EP 0,336,524 for example. A method and a device for storing telecommunication messages are also known from EP 0,304,653.
The task of these installations is that subscribers, who cannot be reached at the moment, initiate a rapid call transfer to the voice mail devices, or a call transfer is initiated after a specified waiting time, if the called subscriber does not answer.
If the transfer is made to a voice mail device and it answers, the telephone signals the number of the called subscriber by means of a Dual Tone Multiple Frequency (DTMF) signals, whereby the calling subscriber is automatically connected with the personal mailbox of the called subscriber.
Now, if all ports of a voice mail device are busy, the subscriber has no possibility of addressing the personal mailbox of the called subscriber. A call-back device is known from EP 0,557,777, which also allows the subscriber to connect with the voice mail device.
Although the calling subscriber can make a call-back to such a mailbox with this call-back device, and after the call-back the calling subscriber is connected with the voice mail device, the calling subscriber is then however placed in the so-called main menu of the voice mail device. Only by again dialing the telephone number of the called subscriber by means of DTMF signals, for which a corresponding telephone set is required, can the calling subscriber be connected with the personal mailbox of the called subscriber.